1. Field of the Invention
This invention relates to a centrifugal type acceleration measuring device, and more particularly a centrifugal type acceleration measuring device in which a turn-table having a measured acceleration transducer mounted thereon is rotationally driven by a motor to apply an acceleration to the acceleration transducer, an output of the acceleration transducer is properly processed for its signal and then the signal is transmitted to a fixed part to perform a measurement of the acceleration in a highly accurate manner.
2. Description of the Related Art
A centrifugal type acceleration measuring device in the prior art is operated such that a turn-table is rotated in a horizontal plane, a measured acceleration transducer (hereinafter called as "an acceleration transducer") is fixed to an outer circumference of the turn-table, the turn-table is rotated, a centrifugal acceleration is given to the acceleration transducer on the turn-table, an output characteristics at this time is inspected and measured.
In such a centrifugal type acceleration measuring device as described above, an induction electric motor is used as a motor for rotationally driving the turn-table, its rotating power is transmitted through a belt, a multi-stage gear box and a clutch or the like and in case of stopping the rotation of the turn-table, a braking action is applied to the motor through a brake.
In addition, a control over the rate of rotation of the motor is also carried out under an open-loop system.
In turn, rotational supporting of the turn-table is also carried out mechanically by a ball bearing.
As the turn-table is rotated, the acceleration transducer detects a centrifugal acceleration. This detected output is transmitted to a measuring system through a signal transmitting system. In this signal transmitting system, an analogue transmitting system performed by means of mechanical contact between a slip ring and a brush due to the fact that the turn-table is being rotated and the measuring system is mounted at a stationary location.
The detected output passed through this transmitting system is inputted into the measuring system in its analogue signal form and converted into a digital signal; thereafter the converted signal passes through an input/output circuit and is inputted to a central processing unit (hereinafter called as "CPU").
After a predetermined analyzing process is carried out at the CPU, a result of analyzing action is displayed at a display device or printed out in a printer.
In addition, electrical power is normally supplied the acceleration transducer disposed on the turn-table through a slip-ring system.
In view of the foregoing, as a calibration method for the acceleration transducer, a comparing calibration system and an absolute calibration system are employed by an official in inspection organization.
The comparing calibration system is operated such that a reference acceleration transducer and a calibrated acceleration transducer are integrally fixed on the same reciprocating vibrator device so as to apply a vibration and the calibrated acceleration transducer is calibrated at a vibration acceleration calculated in response to an output from the reference acceleration transducer.
In addition, the aforesaid absolute calibration system is operated such that a calibrated acceleration transducer is fixed on a reciprocating type vibrator so as to apply a vibration, a displacement amplitude at that vibration is accurately measured by a laser interferometer, a vibration acceleration or the like is calculated in reference to a vibration frequency (number of vibration oscillations per unit time) and then the calculated acceleration is applied as a reference acceleration.
As an additional calibration method of the acceleration transducer, the aforesaid centrifugal type is proposed and this process is not officially acknowledged as a calibration method.
In the prior art centrifugal type acceleration measuring device, at first, an induction motor or the like is used in the rotary driving system for the turn-table, resulting in that a sliding noise of the brush may occur and has a disadvantage that it is mixed in the detected output. In addition, driving transmission is carried out through a belt, a multi-stage gear box and a clutch or the like, resulting in that its size is increased, its vibration is added to the turn-table and then an accurate acceleration is hardly given to the acceleration transducer.
In addition, since the transmitting system for the detected output is also constructed as a mechanical analogue type transmitting system having a slip-ring or a brush, it is not avoidable to have frictional wear at the sliding part, poor contact at the sliding part and overlapping of noise accompanied by the contact on the detected output.
Further, supplying of an electrical power to the measuring system is also carried out by means of sliding system using the slip-ring or a brush, so that its wear is not avoidable.
In turn, in the case the of the acceleration measuring device of the aforesaid comparing type, it has a disadvantage that its calibration accuracy is 2% within a frequency range of 0.5 Hz to 5 KHz and it shows a quite low value of 5% within a frequency range of 5 Hz to 10 KHz.
In addition, the aforesaid absolute calibration system acceleration measuring device has a disadvantage that its calibration accuracy is a high value of about 1% within a frequency range of 20 Hz to 5 KHz and its use can not be carried out at a frequency range of lower than 20 Hz and a desired accuracy may not be satisfactory.
That is, as the device for calibrating the value, it is desirable that its accuracy is high, but in view of its mechanical configuration and a circuit configuration, there is a certain limitation. At present, since an accuracy less than 0.5% is required, it must be said that the aforesaid comparing calibration system measuring device is not adopted as a calibrating device and in turn, in the case of the absolute calibration system measuring device, although this is adopted in a frequency range of 20 Hz to 5 KHz of the calibrating device, a configuration of the calibration system requires a vibrator; a synthesizer and a power amplifier for driving the vibrator; a laser generating device, two fixed mirrors, one vibrating mirror, one beam splitter, an opto-electrical converter, a counter, a filter, a voltmeter for use in detecting a displacement amplitude of vibration; a load amplifier and a voltmeter for measuring an output from a calibrated acceleration transducer; and a computer for controlling in drive of these systems as well as for its calculation and a displaying control or the like, so that it becomes quite complex, large in size and it is expensive and further it has a disadvantage that its measuring operation is complex.
In addition, this absolute calibration system device also has a fatal disadvantage for calibration at a frequency range of 20 Hz or less and 5 KHz or more.